Resolution:
HGA is an I-line style circuit breaker, for mounting only onto I-line panelboards or I-line distribution sections of QED switchboards. It has an I-line connection on one end, and lugs on the other end.
HGL is an Unit mount style circuit breaker, for mounting in devices that do not require an I-line connection. It has lugs on each end of the breaker.
See the picture below to compare them.